The overarching goal of this program is to elucidate fundamental properties of Notch signaling that are central to the pathogenesis of cancer. The Notch pathway is one of perhaps 15 or so signaling pathways that regulate development and tissue homeostasis in metazoan animals and which are frequently deranged in human diseases, including cancer. The clearest example of an oncogenic role for Notch is in T cell acute lymphoblastic leukemia/lymphoma (T-ALL), in which gain-of-function Notchl mutations are common. Notchl is a compelling rational therapeutic target in T-ALL, but attempts to treat T-ALL patients with Notch inhibitors to date have been unsuccessful. Thus, it is apparent that more basic and translational research is needed if Notch-directed therapies are to be effective. With this need in mind, Projects 1 and 2 of this Program have complementary aims focused on filling critical gaps in our basic understanding of how Notchl activates its target genes, which are ultimately responsible for driving T-ALL cell growth and survival. The specific overall objectives of Project 1 and Project 2 are: 1. To determine how Notchl regulates the genomes of T-ALL cells 2. To determine how Notchl regulates the genomes of normal thymocytes The mutations in Notchl that lead to T-ALL often result in ligand-independent proteolysis and receptor activation, but such mutations are rare to non-existent in other cancers. On the other hand, there is abundant evidence that ligand-mediated Notch receptor activation has important roles in cancer, both within tumor cell populations and benign stromal elements, such as endothelial cells and immune cells. Thus, understanding how ligands activate Notch receptors has broad cancer relevance, yet many basic aspects of the events underlying ligand-mediated Notch activation remain unknown. Project 3 will address major gaps in current knowledge by pursuing the following objectives: 3. To test the hypothesis that mechanical force is responsible for Notch receptor activation 4. To understand the molecular logic of ligand endocytosis, an event that is essential for activation of Notch receptors by ligands The goals of the program will be reached in part with the support of a new Bioinformatics Core (Core B) led by Dr. Shirley Liu, an investigator with a strong background in informatics approaches to understanding cancer epigenetics.